Production of xylene hexafluoride



Patented July 24, 195i X asm'res i I I V $2,562,159 I I I I "\PRODUCTIONY'JOF XYtE NEIHEXAFLUORInE ;=?Bruno;H.iWojcik and Aylmer H. Maude, Niagara "Fallsp-N. Y.,- assignors to the United States'- of v-Americaasv represented by the lUnitedtSta-tes V .Atomic Energy Commission --App'lioation November 30,1 944fSerial 'oiai (019260- 651) v. 1 The present-invention removing volatile liquid, products .from= reaction :..vessels,.such as autoclaves, under pressures of .thebrderof. .1,000.lbs. per sq..in. or.--more, and

-.more,particularly to process for removing such .relates; toa process 01".

:.products from. the reaction vessels when there is'v:

-.:.or fluorine derived from hydrogen fluoride ifort- 1' chlorine inchlorinated hydrocarbons.

.We will describe our invention. as appliednto tithe, substitution .of fluorine for :chlorine in -xylene .Hhexachloride. butit is to. be understood that this slowly, allowing ten totwelve hours for -the -op- -eration. Duringthis -time-the :autoclave and its accessories are'bf course unavailable for startingthe next-batch. *The time required for the 5 -reaction itself,-'in'cluding-- the "admissionof hyventing-"01f of the gases *therefore requires-80 "percent -of the time 'of the complete cycle-arid reduces-the effective capacityof ethe expensive equipm ent-involved'- to-a corresponding extent." "We have now found that it'is possibleto in- -crease-the effective "capa'city-0f--the autoclave equipment Joy-about 500-=pereent by transferring "its "liquid and-gaseous contents quickly to a' large but-- relatively inexpensive low pressure receiver, from whiclr-thegases emay be' ventecl in 'three ;.is*mer ely illustrativeand that our invention is..:-:

equally vapplicable -wherever high pressures are involved; and therevisavolatile liquid product.

,In the production ofgxylene .hexafluoride, -.:xylene hexachloride iszreacted With hydrogen -.;fiuoride in an'au-toclave at pressures of unto- 2 ..-about 1600 lbs. .per squin. In this reaction the .hydrogen fluoride .is replaced ..-lov an approximately equal volume of. hydrogen, chloride which ..acc.umulates in the gasfspacesabove the liquid.

quarters of an hourto one hourA In-earrying out this operation with an autoclave of fifteen cubic feet-capacity we-prefer to usea receiver 4 -an-interconnectiong such asa-pipe, -eommunicat- {The X-yene heXachlor-ide and liquid hydro-gen of about seventy-five-eubic feet capacity, having ing with the gas spaces =of the" autoclave and ceiver and also with *a .well pipe extending-t0 near the bottom 0f---the autoclave. .We prefer- 400 lbs. per sq. in.and-.apressureof-about30 -lbswper sqsi'nuhas been-built up in the receiver. e-then allow the liquidproduct" to blow A over throu-gh the well pipe. -W-hen the- -liqu-id fal ls to the mouth of the well :pipe the gas follows it 4 and the pressures become equalized in the auto'clave and; receiver, ataboutl30 to lbs. per- \sq.-1-in. zThe residual::.gas.a.isr quickly :vented ::from the: autoclave and withinqfifteen to-..thinty minutesiit'ais rechargedzandg readvzforrthe next cycle. '-Meanwhile,uthe: gases are being vented .1 product sisowithdrawn. therefrom. ;;If; desired;': the

filled with hydrogen chloride-, mixed with a small excess of whydrogenrfluoride. In.-:an autoclave of fifteen cubic feet capacity in which 525 lbs. ,..o f...xyl ene hexachloride andBOO lbs. of .YHFT have T. been reacted 'togetherto *form'ito xylenehexa- 'i'fluoride and I-IClfthe gases mayhave a volume.

.of. 3600 cubic "feet at atmospheric pressure. Before the product can 'be removed from the i'iautoclaveit is desirable .to. vent .ofi these. gases. I i-Xylene hexafluoride boils.at. 113 C. to 117IC.

the autoclave-'it is'moreoversaturated with the gasea -If the gases werertoabe vented .off.sudgdenly they: would carry with .them a considers-ablegproportion of the product.v It hasttherefore been found desirable to vent off the gases receiver.mayzabezprovidiid w tha restricted vent.

:.wh1ich. canbe leftgjopenwhile-the .prodnntyis being e. remot into :it, .-.-th-,us: .reducing the,-;subsequent time .-;of

-.venti-ng the-receiver.

If preferred, -;the gases. and Jiquid transferredir'om the autoclave; to -the, receiver. in

,I a I :and has a relatively high vapor pressure. In I .two' or:--more .alternations .of. 1 gas and liquid; .or .the, transfer .of atheliquid-may; precedethe Etrans- .ieroofv the gas. .-The:blowing:..d0wn. of; the gases ..,from the receiver requires ..three .quartersotan .hour to one .hQur. One receiver.maytherefoi'e eserve.for, ..-several..autoclaves. ..Thus by a. relativelmsmall. investmentin a,..blow.-.do.wn receiver ,we are able.: to; increaselthe. .effective, capacityof .box (not shown) in cover I. vided with a steam connection 8 and water 2,562,159 i l a 3 an installation of expensive autoclaves by five hundred per cent.

A slightly improved yield in respect of the conversion from hexachloride to hexafluoride is obtained if while the gases are being vented to the receiver, heat is supplied to raise the temperature of the material in the autoclave as may be necessary to maintain the pressure at 1600 lbs. per sq. in. and this is continued until the temperature has reached 140 C. after which the pressure may be allowed to fall as the gases pass over.

The attached drawing illustrates diagram matically a suitable form of apparatus for carrying out the process of the invention.

l is the autoclave, provided with jacket 2, a propeller type agitator 3 and a turbine type agitator 4, driven by motor 5 by means of shaft 6, which issues through a pressure tight stuifing Jacket 2 is prodrawofl 9, controlled by valves and II respectively. Autoclave l is also provided with a well pipe [2, controlled by valve l3, extending through cover 7 to near the bottom of the autoclave, and with a vent pipe 14, controlled by valves l5 and i0, communicating with its interior through cover 1. Pipe i1, controlled by valve 18, is connected to pipe 12 for admission of xylene hexachloride, from a source not shown. Pipe l9, controlled by valve 20, is connected to pipe l2 for admission of hydrofluoric acid from a source not shown. Pipe 2|, controlled by valve 22, is connected to both pipes l2 and M for transfer ofliquid and gaseous products respectively to receiver 23, with which it communicates through its cover 24. Receiver 23 is provided with vent 25, controlled by valve 25, and

passed over, the residual gas pressurein the auto clave is relieved through the same pipe 12, thus equalizing the pressure in the autoclave and receiver. Valve 22 is then closed and the comparativel small quantity of gas in the autoclave quickly vented to the absorptionsystem; through pipe 14 and valves I5 and- I6; after which the autoclave is recharged for the next batch. In the meantime gas has been venting to the absorption system through the orifice plate 30, and this is allowed to continue until the pressure in the receiver has dropped nearly to atmospheric, when valve 26 may be opened. The product is then drawn off through pipe 21.

bottom draw ofi 21, controlled by valve 28.

Vents I4 and 25 are connected to an absorption system for HCl (not shown). Valve 25 may be by-passed by pipe 29, provided with a restricted orifice in plate 30. Thermocouple 3| is let in through cover 1 to the interior of the autoclave. ,Pressure gauge 32 is connected to pipe [4 and pressure gauge 33 to pipe 2!.

With valves l3, l5 and I6 open and valves 20 and 22 closed, a weighed quantity of xylene hexachloride is charged into autoclave I through valve l8 and pipe 12, so as to leave an adequate gas space above the liquid. With valves l5 and [6 closed, and with the agitator operating, hydrofluoric acid is admitted below the surface of the liquid through pipes l9 and I2 and valves 20 and 1 13. Steam is then admitted to the jacket. When the temperature of the liquid has reached C.,

as shown by thermocouple 3|, the reaction begins. 'With the heat of reaction, augmented by heat from the jacket, the temperature continues to rise. When it has reached 110 C., it is held constant at that temperature by control of the steam in the jacket. At this temperature the pressure builds up to 1600 lbs. per sq. in, as

indicated by gauge 32. The reaction is thus caused to proceed as above described. At the conclusion of the reaction, with all other valves controlling receiver 23 closed, valves [5 and 22 are opened, permitting the by-product HCl to flow into the receiver through pipe 2|, until the pressure in the autoclave has fallen to about 400 lbs. per sq. in., the corresponding pressure in receiver '23, as indicated by gauge 33, being about 30 lbs.

} per sq. in. Valve 15 is then closed and valve 13 opened, causing the liquid to be transferred to the receiver. When the last of the liquid has Although the present invention has been described with reference to preferred embodiments and examples, it will be understood that variations and modifications may be made therein and equivalents substituted therefor without departing from the spirit of the invention.

We claim as our invention:

In a method for producing xylene hexafiuoride and hydrogen chloride by the reaction of hydrogen fluoride upon xylene hexachloride in an autoclave under attained pressures of at least 1000 pounds per square inch, the process of rapidly removing the liquid xylene hexafluoride from the autoclave without losing considerable amounts of liquid xylene hexafiuoride by entrainment with the gaseous hydrogen chloride which comprises venting gaseous hydrogen chloride from the top of said autoclave to a receiver having a volume about five times the volume'of said autoclave until the gas pressure in said autoclave has been reduced to about one quarter of its attained value, utilizing the residual gas pressure in the autoclave to blow the liquid xylene hexafluoride from near the bottom of the autoclave upward into a well pipe and over into said receiver, bleeding gaseous hydrogen chloride from said autoclave to said receiver after the liquid xylene hexafluoride has been blown over into said receiver until the gas pressures in said autoclave and said receiver become equal, shutting off the fluid connection between said autoclave and said receiver, separately and quickly venting the remaining gaseous hydrogen chloride from said autoclave,

slowly venting the gaseous hydrogen chloride from said receiver while said autoclave is being recharged, and withdrawing liquid xylene hexafluoride from the bottom of said receiver after substantially all of the gaseous hydrogen chloride has been vented therefrom.

BRUNO H. WOJCIK, AYLMER H. MAUDE.

REFERENCES CITED The following references are of record in the file of this patent: 

